Drug repurposing is an effective approach to identify active drugs with known toxicity profiles for rare
cancers such as ACC. The objective of this study was to determine the anticancer activity of combination treatment for ACC from previously identified candidate agents using quantitative high-throughput screening (qHTS). In this study, we evaluated the anticancer activity of
flavopiridol and
carfilzomib in three ACC cell lines in vitro and in vivo. Human ACC samples were analyzed for drug-target analysis, and
cancer-related pathway arrays were used to identify
biomarkers of treatment response. Because
flavopiridol is a potent
cyclin-dependent kinase (CDK) inhibitor, we found significantly higher CDK1 and CDK2
mRNA expression in three independent cohorts human ACC (p<0.01) and CDK1
protein by immunohistochemistry (p<0.01) in human ACC samples. In vitro treatment with
flavopiridol and
carfilzomib in all three ACC cell lines resulted in a dose-dependent, anti-proliferative effect, and the combination had synergistic activity as well as in three-dimensional
tumor spheroids. We observed increased G2M cell-cycle arrest and apoptosis with combination treatment compared to other groups in vitro. The combination treatment decreased
XIAP protein expression in ACC cell lines. Mice with human ACC xenografts treated with
flavopiridol and
carfilzomib had significantly lower
tumor burden, compared to other groups (p<0.05). We observed increased cleaved-
caspase expression and decreased XIAP in
tumor xenografts of mice treated with combined agents. Our preclinical data supports the evaluation of combination
therapy with
flavopiridol and
carfilzomib in patients with advanced ACC.